1. Field of the Invention
The present invention relates to a circuit breaker device for cutting off the output of electric energy from a battery power supply on an electric vehicle, and more particularly to a circuit breaker device which can be operated highly reliably for cutting off the output of electric energy from a battery power supply on an electric vehicle.
2. Description of the Prior Art
Japanese Laid-Open Patent Publication No. 53-140551 discloses a conventional circuit breaker device having a breaker including a single shunt coil connected to a power supply. Depending on signals from various sensors connected to the circuit breaker device, a current flows through the shunt coil to open breaker contacts to which the power supply and circuits are connected, for thereby turning off the power supply and disconnecting the circuits to protect the circuits.
The conventional circuit breaker device is arranged to operate in response to the signal from any one of the sensors.
Since the conventional circuit breaker device has only one shunt coil and one power supply is connected to the shunt coil, it may be possible, upon a voltage drop of the power supply, for the circuit breaker device to fail to be tripped and hence to fail to turn off the power supply even when a current flows through the shunt coil based on the signal from any one of the sensors.
Electric vehicles generally have batteries as a power source which includes a drive power supply for applying a high voltage ranging from 150 V to 300 V to energize a motor and an accessory power supply for applying a low voltage of 12 V to energize accessories and a controller of the circuit breaker device. These power supplies are highly likely to experience a voltage drop quickly due to rapid energy consumption from the batteries. In particular, the voltage of the accessory power supply suffers a voltage drop more often than the drive power supply when the driver of the electric vehicle forgets to turn off the head lamps.
In the case where only the accessory power supply is connected to the shunt coil of the circuit breaker device for supplying a current therefrom to the shunt coil to open the contact of the circuit breaker device based on a sensor coil, the circuit breaker device may not be tripped in the event of a voltage drop of the accessory power supply.
Inasmuch as the controller of the circuit breaker device is energized by the accessory power supply, the controller may not operate properly owing to a voltage drop of the accessory power supply when the stored electric energy is excessively consumed. It is therefore desirable in an electric vehicle having a high-voltage power supply for applying a high voltage ranging from 150 V to 300 V to be able to monitor the operation of the electric vehicle and also monitor the condition of the high-voltage power supply until its voltage drops to a level which is too low for the high-voltage power supply to function properly.